In such locking devices, the locked and unlocked positions of the bolt are generally determined by simply stopping the electric motor that rotates the drive rod. This may for example be achieved by the provision of interrupters which are actuated, for example, by a cam which is coupled to the bolt, and which transmits pulses to an electronic circuit for controlling the motor. This circuit then cuts off the power supply to the motor.
However, between the instant at which the power supply to the motor is cut off and the effective cessation of rotation of the motor shaft, a time interval elapses. It is difficult to forecast the duration of this time interval, which depends, in particular, on the inertia of the moving parts of the motor and on various friction effects that occur within the locking device. Accordingly, there is always some uncertainty as to the effective unlocked position of the bolt, and this disadvantage is amplified by the fact that this position varies every time the motor is stopped.